In one basic type of ink jet head, ink drops are produced on demand. Exemplary drop-on-demand ink jet heads are illustrated in U.S. Pat. No. 4,106,032 issued to Miura et al. and U.S. Pat. No. 4,727,378 issued to Le et al. These ink jet heads produce an ink drop at an ink-drop forming aperture. The ink drop is propelled through an air chamber toward a main external aperture of the ink jet head. Air under pressure is delivered to the air chamber and entrains the drop of ink in a generally coaxial air stream as the ink drop travels through the air chamber.
During printing, drops of ink tend to collect in and around the ink jet apertures. When the ink does build up, it can prevent drop ejection, or cause improper ink drop trajectory and nonuniformity in ink drop size. It therefore becomes imperative that the aperture area be cleansed of excess ink periodically in order to maintain a consistently clean aperture during printing.
A similar ink jet head is described in U.S. Pat. No. 4,598,303 issued to Peekema et al. wherein the tendency of ink to collect around the ink jet orifice is maintained in order to standardize drop size and trajectory. These types of heads are purged by flooding the air chamber with ink to remove contaminants and air bubbles from the ink chamber and system. The unwanted ink is then expelled from the air chamber into a waste reservoir using the air pressure system. Such purging is disclosed in the Le et al. patent as well as in a service manual for a color graphics copier having model number 4692 made by Tektronix, Inc. of Beaverton, Oreg.
Apparatus has also been designed for cleaning the external face of the print head around the outer orifice. For instance physical wipers, such as squeegees and cloth wipes are moved across or blotted against the face. It is possible for such apparatus to leave some part of the cleaner substance in the aperture.
One conventional external type of cleaner is described in German Patent Application No. DE 319704 Al based on a prior Japanese Patent Application No. JP P 136165/86. This cleaner provides an enlarged cavity placeable against the face of a print head adjacent the ink jet apertures. Gas is directed at the aperture with an absorbent material disposed in the cavity and positioned below the aperture for catching ink blown down from around the aperture.
This device doesn't necessarily provide a well defined flow past the aperture for several reasons. Firstly, a seal is not developed between the cavity and the aperture face, so that the gas and ink carried by the gas can travel through the space between the print head and the body forming the cavity. Secondly, since a control volume for the impinging air stream from the air jet nozzle is not completely defined by solid boundaries, the air flow will be diverted in all directions when the air stream impinges upon the ink jet head. Thus, the gas flow is uncontrolled and tends to be dispersed. This dispersion creates inconsistency in the effectiveness of the fluid stream to carry the ink from the aperture.
The present invention provides an external ink jet print head cleaner that maintains controlled fluid flow into the cleaning region, around an ink jet aperture and out of that region without contacting the aperture region with a solid substance. The term fluid as used herein refers to both liquid and gas. In particular, a continuous well-defined passageway is provided that directs a fluid smoothly past the aperture so that the pressure, mass flow and directionality of the fluid is controlled in the vicinity of the aperture, thereby assuring effective removal of the ink drops in the area of the aperture and complete removal of ink from the print head.
This is provided by a body having a first face placeable against the print head face. This first face has an opening sized to surround the ink jet aperture when the first face is placed against the print head face. Means are provided in the body which define a cavity extending along the opening and having an inlet disposed adjacent to one edge of the opening. An outlet is disposed adjacent to a generally oppositely disposed edge of the opening. The cavity preferably has a depth away from the opening less than the length of the opening between the inlet and outlet. Finally, means are provided for directing a volume of a fluid through the inlet into the cavity and out the outlet.
The present invention also provides a method of cleaning the aperture disposed in the face of an ink jet print head. This method includes enclosing the aperture of the print head with a cavity formed in a body with a first face having an opening facing the print head face, an inlet disposed adjacent to one edge of the opening, and an outlet disposed adjacent to a generally oppositely disposed edge of the opening. A fluid supply is directed through the inlet and cavity at an angle that is substantially tangential to the aperture, and out the outlet. thereby carrying ink disposed around the apertures out through the outlet.
It can be seen that the present invention provides a simple, effective ink jet aperture cleaner. The fluid directed substantially tangentially past the aperture is maintained in a controlled fashion in a substantially unidirectional flow by a reduced cavity forming an enclosure around the apertures. These and other features and advantages of the present invention will become apparent from a reading of the following detailed description of the preferred embodiment in conjunction with the accompanying drawings.